This section provides background information related to the present disclosure which is not necessarily prior art.
A model of a typical ultrasonic metal welding apparatus 100 is shown in FIG. 1. Typical components of ultrasonic metal welding apparatus 100 include an ultrasonic transducer 102, a booster 104, and an ultrasonic horn 106. As is commonly understood by those of skill in the art of ultrasonic welding, an ultrasonic horn is a metal bar that transfers mechanical energy from the ultrasonic transducer to the work piece. The ultrasonic horn is typically one-half wavelength long at the resonant frequency at which the ultrasonic transducer driving the horn resonates. Electrical energy from a power supply 101 at a frequency of 20-60 kHz is converted to mechanical energy by the ultrasonic transducer 102. The mechanical energy converted in the ultrasonic transducer 102 is transmitted to a weld load 108 (such as two pieces of metal 112, 114) through the booster 104 and the horn 106. The booster 104 and the horn 106 perform the functions of transmitting the mechanical energy as well as transforming mechanical vibrations from the ultrasonic transducer 102 by a gain factor.
The mechanical vibration that results on a horn tip 110 is the motion that performs the task of welding metal together. Horn tip 110 may be made of tungsten carbide or other high strength, hard material. The metal pieces 112, 114 to be welded together are placed adjacent to the horn tip 110. The horn tip 110 is brought into contact with top metal piece 112 to be welded. In the embodiment of FIG. 1, horn 106 includes two horn tips 110, one of which is brought into contact with top metal piece 112. The axial vibrations of the horn 106 now become shear vibrations to the top metal piece 112. The shear vibrations are transmitted to the top metal piece 112, causing it to move back and forth with respect to bottom metal piece 114 causing surfaces of the two metal pieces abutting each other at a weld interface to be heated, eventually melting together. A weld anvil 120 grounds the bottom metal piece 114. It should be understood that such an ultrasonic welder can be used to weld multiple metal foil layers together, such as several layers of aluminum or copper foil.
A similar apparatus is used in ultrasonically welding plastic pieces together. The principal difference is that the ultrasonic horn oscillates in a manner to impart vertical oscillations in the plastic pieces. That is, the ultrasonic horn causes oscillatory compression/decompression of the plastic pieces with respect to each other causing surfaces of the plastic pieces abutting each other at a weld interface to be heated, eventually melting together.
Ultrasonic welders are for example disclosed in U.S. Pat. No. 5,658,408 for Method for Processing Workpieces by Ultrasonic Energy;” U.S. Pat. No. 6,863,205 for Anti-Splice Welder,” and U.S. Pat. Pub. No. 2008/0054051 for “Ultrasonic Welding Using Amplitude Profiling.” The entire disclosures of the foregoing are incorporated herein by reference.
Ultrasonic horns are key components of ultrasonic welders. In ultrasonic welding of metal and plastic films and fabric, ultrasonic horns are a wear item in that the tip of the ultrasonic horn that contacts the work piece being welded wears over time. This requires that the ultrasonic horn be periodically replaced, which adds cost to the ultrasonic welding process since ultrasonic horns are relatively expensive components. To reduce this cost, certain ultrasonic horns have replaceable tips. One type of replaceable tip has an outer contact portion and a threaded stud extending therefrom that is tightened into a threaded bore in the end of the ultrasonic horn to secure the replaceable tip to the ultrasonic horn. In another type, the end of the ultrasonic horn has a stud projecting outwardly therefrom over which the replaceable tip fits. An end portion of the stud is threaded and a front nut is then tightened on the threaded end portion the stud against a front surface of the replaceable tip to secure the replaceable tip to the end of the ultrasonic horn.